Electrophysiologic recording provides inexpensive and non-invasive monitoring of both normal and pathological human brain function. With a saline-sponge technology, a dense array of 64,128, or 256 electrodes can be applied in a few minutes, allowing electroencephalographic (EEG) recording in emergency and intensive care settings. However, EEG evaluations in demanding clinical settings often require long-term monitoring, and the current sponge-saline electrode technology provides usable EEG for only 2-3 hours before re-hydration is required. Long-term recordings can be accomplished by the use of conventional electrode pastes or glues, but the discomfort and preparation time become major impediments in many medical settings for which brain monitoring may be useful. This Phase II proposal follows on the successful completion of the Phase I project, which demonstrated the ability to build an EEG electrolyte based on stimulus-responsive hydrogel technology. The Phase II project proposes the refinement of this novel Phase- Reversible Electro-Physiological Sensor (PREPS) electrolyte technology that will permit long-term recording with dense electrode arrays to be fast and comfortable. PREPS technology allows for the manipulations of the electrolyte with either electric current or temperature to achieve both skin bonding and skin hydration to produce high quality extended EEG monitoring. Based on the Phase I results, this Phase II project will perform systematic refinement studies to optimize the PREPS technology for dermal EEG applications and develop and test protocols for PREPS in clinical settings.